Light absorbent agent polymer useful for organic anti-reflective coating, its preparation method and organic anti-reflective coating composition comprising the same

ABSTRACT

Disclosed are a light absorbent agent polymer for organic anti-reflective coating which can prevent diffused light reflection of bottom film layer or substrate and reduce standing waves caused by a variation of thickness of the photoresist itself, thereby, increasing uniformity of the photoresist pattern, in a process for forming ultra-fine patterns of photoresist for photolithography by using 193 nm ArF among processes for manufacturing semiconductor devices, and its preparation method. Also, the present invention discloses an organic anti-reflective coating composition comprising a light absorbent agent polymer for the organic anti-reflective coating and a pattern formation process using the coating composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light absorbent agent polymer usefulfor organic anti-reflective coatings which can prevent diffused lightreflection of the bottom film layer or substrate and reduce standingwaves caused by a variation of thickness of the photoresist itself,thereby, increasing uniformity of the photoresist pattern, in a processfor forming ultra-fine patterns of photoresist for photolithography byusing 193 nm ArF among various processes for manufacturing semiconductordevice, and its preparation method.

Also, the present invention provides an organic anti-reflective coatingcomposition (hereinafter abbreviated as “the coating composition”)comprising the light absorbent agent polymer for the organicanti-reflective coating (hereinafter abbreviated as “the coatingpolymer”) and a pattern formation process using the coating composition.

2. Description of the Related Art

In a fabrication process of ultrafine patterns for preparingsemiconductor devices, standing waves and reflective notching inevitablyoccur due to the optical properties of lower film layer on thephotoresist film and due to the thickness changes in the photosensitivefilm. In addition, there is another problem in that a CD (criticaldimension) alteration is caused by diffracted and reflected light fromthe lower film layers. Thus, it has been suggested to introduceanti-reflective coating that prevents back reflection of a lower filmlayer between a lower film and a photoresist by introducing organicmaterial with high absorbance at a wavelength range of the lightemployed as a light source.

Especially, when exposed to UV light from the light source, aphotoresist thin film is transmitted by the UV light, thus allowing thelight absorbed in bottom portion of the thin film to be scattered and/orreflected. Such an anti-reflective coating can absorb the scatteredand/or reflected light and, thereby, directly affecting the fineprocessing of the photoresist.

Anti-reflective coatings are classified into inorganic and organicanti-reflective coatings depending upon the material used, or asabsorptive and interfering anti-reflective coatings based on theoperation mechanism. For a fine pattern forming process using I-line(365 nm wavelength) radiation, inorganic anti-reflective coating arepredominantly used, while TiN and amorphous carbon (a-C) are employed asan absorptive system anti-reflective coating and SiON are employed as aninterfering system anti-reflective coating. In a fabrication process ofultrafine patterns using KrF light (248 nm), an inorganicanti-reflective coating has been mainly used and an organicanti-reflective coating has been used occasionally along with theinorganic anti-reflective coating.

However, in an ultra-fine pattern forming process using ArF light (193nm), no proper anti-reflective coating has been developed yet.Especially, in the case of an inorganic anti-reflective coating, nomaterial has been known which enables the control of the interference at193 nm, the wavelength of the light source. Thus, there has been greatdeal of efforts to employ an organic compound as an anti-reflectivecoating.

To be a good organic anti-reflective coating, the following conditionsmust be satisfied.

First, an anti-reflective coating must not be dissolved by a solvent ofthe photoresist in the process of laminating an anti-reflective coatingand then coating photoresist on the top portion thereof. In order toachieve this goal, such an anti-reflective coating must be designed toform a cross-linked structure without producing any chemical by-product,in a process of lamination an anti-reflective coating by coating ananti-reflective coating composition and then performing a bakingprocess.

Second, in order to prevent diffused light reflection from a bottom filmlayer, the coating must contain certain materials to absorb light at thewavelength range of the exposure light source.

Third, no flowing in and out by chemicals such as acid or amine occurfrom the anti-reflective coating. This is because when acid migratesfrom anti-reflective coating to a photoresist film of an unexposedportion, undercutting occurs at a lower part of the pattern whilefooting may occur when a base, such as amine, migrates to thephotoresist film. Such a phenomenon can be stopped by preventing suchchemicals from coming in or going out of the anti-reflective coating.

Fourth, the etching speed of the anti-reflective coating should befaster than the etching speed of the upper photosensitive film so as tofacilitate an etching process by using photosensitive film as a mask.

Finally, the anti-reflective coating must be as thin as possible to anextent as to sufficiently play a role as an anti-reflective coating.

In order to satisfy the above requirements, conventional organicanti-reflective coating compositions generally comprise a cross-linkingagent to allow the anti-reflective coating to have a cross-linkedstructure, a light-absorbing agent to absorb the light at the wavelengthrange of exposure light source, a thermal acid generator as a catalystfor activating the cross-linking reaction, and an organic solvent.

As mentioned above, it strongly requires a novel organic anti-reflectivecoating preferably useable as the anti-reflective coating for the ArFlight source at 193 nm, which can control the interference phenomenon tothe ArF light source. Therefore, the present inventors have developed ananti-reflective coating polymer capable of controlling the interferencephenomenon to the ArF light source, as well as to satisfy all of therequirements mentioned above, and a composition comprising the coatingpolymer, thereby accomplishing the present invention.

SUMMARY OF THE INVENTION

The present invention is designed in consideration of the problems ofprior art mentioned above, and therefore it is an object of the presentinvention to provide a novel polymer useable as a light absorbent agentfor an organic anti-reflective coating in an ultrafine pattern formingprocess by using an ArF light source with 193 nm wavelength in asemiconductor device production process, and its preparation method.

In another aspect, it is another object of the present invention toprovide an organic anti-reflective coating composition comprising theorganic anti-reflective coating polymer, a pattern forming method usingthe same and a semiconductor device produced by the pattern formingmethod.

To achieve the above objects, the present invention provides a lightabsorbent agent polymer for an organic anti-reflective coatingrepresented by the following the general formula I and having a weightaverage molecular weight in the range of 5,000 to 15,000.

wherein a and b represent the mole percent of respective monomers anda:b=5 to 95% by mole:5 to 95% by mole.

The polymer of formula I contains chromophore having a high absorbanceat the wavelength of 193 nm, and comprises maleic anhydride as a monomerto sufficiently form a cross-linkage bond with a cross-linking polymerhaving an acetal functional group. Because of such characteristics, thepolymer of formula I can be preferably used as the light absorbent agentin the organic anti-reflective coating composition with respect to thelight source having 193 nm wavelength. That is, since the polymer offormula I is included in the coating composition for serving as thelight absorbing agent, it can control the light interference phenomenonduring the ultra-fine pattern formation process using the 193 nm lightsource. In addition, the polymer can easily form a cross-linkage bondwith the cross-linking polymer to give solvent-resistant ability to theanti-reflective coating, thereby ensuring improved photoresist patternsby employing the coating composition containing such light absorbentagent to form the anti-reflective coating.

As mentioned above, the polymer of formula I has a molecular weightranging from 5,000 to 15,000. If the molecular weight is less than5,000, no sufficient cross-linkage bond will be generated on the formedanti-reflective coating and lead to the decrease in thesolvent-resistance of the anti-reflective coating. If the molecularweight is higher than 15,000, the viscosity of the polymer becomeshigher, thereby causing difficulty in producing the anti-reflectivecoating composition resulting in trouble with respect to the applicationof the anti-reflective coating composition.

The polymer of the formula I may be prepared by dissolving a maleicanhydride and 5-hydroxy-2-methyl-1,4-naphthoquinone in an organicsolvent, adding a polymerization initiator to the dissolved material,then, conducting free-radical polymerization under vacuum conditions, at60 to 70° C. for 6 to 12 hours.

The organic solvent for polymerization used in such preparation methodpreferably includes at least one selected from a group consisting oftetrahydrofuran, cyclohexanone, dimethyl formamide, dimethyl sulfoxide,dioxane, methylethylketone, PGMEA, ethylacetate, benzene, toluene andxylene. The polymerization initiator used in the above method includesall of conventional radical initiators for free-radical polymerizationand, preferably, at least one selected from a group consisting of2,2′-azobisisobutyronitrile (AIBN), benzoyl peroxide, acetyl peroxide,lauryl peroxide, t-butyl peracetate, t-butyl hydroperoxide anddi-t-butyl peroxide.

In another aspect of the present invention, there is provided an organicanti-reflective coating composition comprising: a light absorbent agentpolymer represented by the following formula I and having an averagemolecular weight in the range of 5,000 to 15,000; a cross-linkingpolymer represented by the following formula II and having a weightaverage molecular weight in the range of 2,000 to 70,000; a thermal acidgenerator; and an organic solvent.

wherein a and b represent the mole percent of the respective monomersand a:b=5 to 95% by mole:5 to 95% by mole.

wherein R₄ and R₅ represent independent alkyl groups having 1 to 10carbon atoms substituted by branched chain or main chain; R₃ is hydrogenor methyl group; and c:d=5 to 90% by mole:10 to 95% by mole.

Briefly, the above coating composition of the present inventioncomprises the polymer represented by formula I as the light absorbentagent, in which the maleic anhydride group contained in the polymer offormula I can generate a cross-linkage bond with the acetal functionalgroup contained in the cross-linking polymer of formula II, whereby theformed anti-reflective coating has sufficient solvent-resistance. Also,by such a cross-linkage bond, it is possible to protect chemicalmaterials such as acid or amine from being transferred out of theanti-reflective coating, to, in turn, minimize under-cutting and/or aputting phenomenon resulting in formation of the improved photoresistpattern. Furthermore, both of the polymers represented by the formulae Iand II comprise a chromophore having a remarkably high absorbance toabsorb light reflected or diffused at bottom portion of the photoresistfilm and to significantly reduce the standing wave effect caused by suchreflected and/or diffused light.

Such polymer of the formula II has been disclosed in Korean PatentApplication No. 2002-73648 filed by the applicant of the presentinvention, which is enclosed herewith in reference to a practicalprocedure for producing the same and characteristics thereof.

In the organic anti-reflective coating composition according to thepresent invention, such cross-linking polymer of the formula IIpreferably comprises at least one selected from a group consisting ofpolymers having the structures of formulae III to VI.

wherein a:b=5 to 90% by mole:10 to 95% by mole.

In particular, since the polymers of formulae III to VI can activelygenerate the cross-linkage bonds with the light absorbent agent polymerhaving a maleic anhydride group in the presence of acid, it can bepreferably employed as a cross-linking agent in the organicanti-reflective coating composition according to the present invention.

With respect to the organic anti-reflective coating composition of thepresent invention, such thermal acid generator may be the one generallyused in conventional organic anti-reflective coating compositions and,preferably comprises a compound having a structure represented by thefollowing formula VII.

The thermal acid generator serves as a catalyst for activating suchcross-linking reaction between the above cross-linking agent and thelight absorbent agent. When a thermal process such as the baking processis carried out after applying such thermal acid generator on a wafer,acid is generated from the thermal acid generator and, in the presenceof acid generated by the above process, the cross-linking reactionbrings out to form the organic anti-reflective coating insoluble in thesolvent for the photoresist. In other words, it is possible toaccelerate the cross-linking reaction between the light absorbent agentand the cross-linking agent by employing the compound in formula VII asthe thermal acid generator.

The organic solvent used in the organic anti-reflective coatingcomposition of the present invention preferably includes at least oneselected from a group consisting of methyl 3-methoxy propionate (MMP),ethyl 3-ethoxy propionate (EEP), propyleneglycol methylether acetate(PGMEA) and cyclohexanone.

In the organic anti-reflective coating composition of the presentinvention, the amount of the polymer represented by formula I as thelight absorbent agent is preferably in the range of 0.3 to 70% by weightwith respect to the organic solvent contained in the anti-reflectivecoating composition and the amount of the polymer of formula II as thecross-linking agent is preferably in the range of 0.3 to 50% by weightwith respect to the organic solvent contained in the anti-reflectivecoating composition. Likewise, the amount of the thermal acid generatoris 0.5 to 40% by weight with respect to the total amount of the lightabsorbent agent and the cross-linking agent.

Therefore, when a baking process is carried out after applying theorganic anti-reflective coating composition comprising such componentsmentioned above with the composition rates on the wafer, acid isgenerated from the thermal acid generator and, the cross-linkingreaction brings out between the light absorbent agent polymer of formulaI and the cross-linking agent polymer of formula II by the acidgenerated from the above process to form the organic anti-reflectivecoating. Such organic anti-reflective coating can absorbdistant-ultraviolet (DUV) ray transmitting the photoresist film andreaching to the organic anti-reflective coating, thereby preventingdiffused light reflection from the bottom layer of the photoresist film.

In this case, the organic anti-reflective coating becomes insoluble inthe photoresist solution to be applied over the coating because of across-linkage bond formed between both of the polymers with the formulaeI and II.

In a further aspect of the present invention, there is provided a methodfor forming pattern on a semiconductor device comprising the steps of:(a) coating the organic anti-reflective coating composition of thepresent invention on top portion of a film layer to be etched; (b)conducting the baking process for the obtained material to generate thecross-linkage bond and form the resultant organic anti-reflectivecoating; (c) applying a photoresist on the top portion of the organicanti-reflective coating, exposing and developing the photoresist film toproduce the desired photoresist pattern; (d) etching the organicanti-reflective coating by using the obtained photoresist pattern as anetching mask, in turn, the film layer to be etched, thereby forming apattern on the film layer to be etched.

The patterning process of the present invention, the baking process ispreferably performed at 150 to 250° C. for 1 to 5 minutes.

With respect to the patterning process of the present invention, theprocess may further comprise an additional baking process before orafter the exposure process, which is preferably conducted at 70 to 200°C.

Although the anti-reflective coating composition and the patterningprocess according to the present invention are mostly adapted to anultrafine pattern formation processes using an ArF light source, theycan be also applied to other ultrafine pattern formation processes usingKrF, DUV including EUV, E-beam, X-ray or an ionic beam.

In a still another aspect of the present invention, there is provided asemiconductor device produced by the patterning process according to thepresent invention mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the present invention will become apparentfrom the following description of examples with reference to theaccompanying drawing in which:

FIG. 1 is an electron microscopic photograph illustrating a patternformed by a pattern formation process according to one example of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT EXAMPLES

The present invention is now described in a further detail withreference to examples, which are only illustrative and are not intendedto limit the scope of the invention in any way.

Example 1 Synthesis of Light Absorbent Agent Polymer

20 g of maleic anhydride and 19 g of5-hydroxy-2-methyl-1,4-naphthoquinone (0.5% by mole per maleicanhydride) were dissolved in 26 g of PGMEA. The dissolved mixture wasadded with 0.5 g of AIBN to form a vacuum condition then reacted at 65°C. for 7 hours. After completing the reaction, the solvent was removedfrom the obtained solution by means of an evaporator. Thereafter, thetreated solution was under deposition and filtration processes indistilled water, then washed by using ethylether several times toproduce the light absorbent agent polymer of formula I (yield 40%).

Molecular weight: 7,000

Example 2 Preparation of Organic Anti-Reflective Coating Composition

1 g of the light absorbent agent polymer prepared from Example 1 and 0.4g of the cross-linking agent polymer of formula III were dissolved in asolvent mixture comprising 4 g of propylene glycol methylether acetatesolvent; 10 g of methyl 3-methoxy propionate solvent; 10 g of2-heptanone solvent; and 7 g of tetrahydrofurane solvent. After adding0.1 g of the thermal acid generator having the structure represented bythe formula VII to the resultant material to be dissolved, the dissolvedmixture passed through a filter to produce the desired organicanti-reflective coating composition.

Example 3 Formation of Organic Anti-Reflective Coating and PhotoresistPattern

On a silicone wafer, a spin-coating was carried out with the organicanti-reflective coating composition prepared in Example 2, then a bakingprocess was conducted for the obtained material at 215° C. for 2 minutesto generate a cross-linkage bond and form the desirable anti-reflectivecoating. Thereafter, the obtained anti-reflective coating was put undera coating process with a so-called Keum Ho petroleum photosensitiveagent (the name of generally used photoresist materials) and anotherbaking process at 110° C. for 90 seconds. After conducting the abovebaking process, the baked product was exposed to a light source by meansof ASML/900 scanner apparatus, then, under an additional baking processat 130° C. for 90 seconds. The exposed wafer was developed using anaqueous solution of 2.38% by weight of TMAH. From the developed materialproduced was the pattern shown in FIG. 1.

As above mentioned, the present invention provides a polymer of formulaI useable as a light absorbent agent for organic anti-reflective coatingcomposition, which can form a cross-linkage bond with a cross-linkingpolymer containing acetal groups effective in providingsolvent-resistance to the finalanti-reflective coating and to preventunder-cutting and/or putting phenomena. Furthermore, the polymer offormula I comprises a chromophore having higher absorbance to 193 nmlight source, thereby efficiently controlling the interferencephenomenon of light at such light source.

Briefly, according to the present invention, it is possible to providean organic anti-reflective composition comprising the polymer mentionedabove and a pattern formation process using the same, whereby animproved perpendicular pattern can be obtained in an ultra-fine patternformation processes using 193 nm light source, and the present inventioncan significantly contribute to the high integration of semiconductordevice.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. An organic anti-reflective coating composition comprising: a lightabsorbent agent polymer represented by the following formula I; across-linking polymer represented by the following formula II; thermalacid generator; and an organic solvent:

wherein each of a and b represents the mole percent of respectivemonomers and a:b=5 to 95:5 to 95:

wherein R₄ and R₅ represent independently alkyl groups having 1 to 10carbon atoms substituted by branched chain or main chain; R₃ is hydrogenor methyl group; c and d represent the mole percent of respectivemonomers and c:d=5 to 90:10 to
 95. 2. The composition according to claim1, wherein the polymer represented by the formula II comprises at leastone selected from a groups consisting of polymers having the structuresof the following formulae III to VI:

wherein a:b=5 to 90% by mole:10 to 95% by mole.
 3. The compositionaccording to claim 1, wherein the thermal acid generator comprises thecompound having the structure of the following formula VII:


4. The composition according to claim 1, wherein the organic solventcomprises at least one selected from a group consisting of methyl3-methoxy propionate (MMP), ethyl 3-ethoxy propionate (EEP),propyleneglycol methylether acetate (PGMEA) and cyclohexanone.
 5. Thecomposition according to claim 1, wherein the amount of the lightabsorbent agent is 0.3 to 70% by weight with respect to the organicsolvent contained in the organic anti-reflective coating composition andthe amount of the cross-linking agent in an amount ranging from 0.3 to50% by weight with respect to the organic solvent contained in theorganic anti-reflective coating composition.
 6. The compositionaccording to claim 3, wherein the thermal acid generator is 0.5 to 40%by weight with respect to total amount of the light absorbent agent andthe cross-linking agent.